Generally, a pressure-type contact switch operates to turn on/off power supply applied to a pressure pump using expansion and contraction of a bourdon tube connected to a discharge conduit, according to change in water-pressure passing the discharge conduit by means of the pressure pump.
In the pressure-type contact switch described above, a movable support is installed between two contact points. The movable support rotates to move toward one contact point to thereby turn on the pressure pump when the pressure in the bourdon tube decreases, whereas the movable support rotates to move toward the other contact points to thereby turn off the pressure pump when the pressure in the bourdon tube increases.
The pressure-type contact switch for use in operation and cessation of the pressure pump begins or ceases the operation of the pressure pump according to on-state or off-state of the contact points. Here, the contact points might be damaged and the pressure pump could operate incorrectly, because the on/off-states of the contact points are continuously repeated due to instantaneous change in pressure according to the operation and the cessation of the pressure pump.
In order to avoid the above-described problem, it is possible to include a magnetic maintenance circuit within a start circuit of the pressure pump, which maintains on/off-state for a certain period of time. However, the magnetic maintenance circuit is a high-priced item, so that it increases the manufacturing cost of the contact switch.